1. Field of the Invention
This invention relates to a semiconductor device, and more particularly to a semiconductor device provided with a surface passivation layer which is indispensible for the construction of diode and transistors having high reliability.
2. Description of the Prior Art
The surface passivation layer is generally formed by the vapor growth method. Studies have been made on the material of the surface passivation layer in order to make semiconductor elements more passive and more stable. Passivating layers of silicon dioxide SiO.sub.2 and SiO.sub.2 containing phosphorus, widely used. However, such passivating layer have not sufficient resistant againt moisture. Under moist conditions, leakage currents vary.
A SiO.sub.2 layer is coated on the PN junction of the diode which is exposed at the surface of a silicon semiconductor substrate. However, in operation, an undesirable memory function is induced by the positive charge like sodium ion existing in the SiO.sub.2 layer. A channel is formed in the P-type semiconductor substrate, due to the negative charge induced by the positive charge in the SiO.sub.2 layer.
Accordingly, the SiO.sub.2 layer has undesirable characteristics. Moreover, the surface region of Si is apt to be distorted due to the difference between the thermal expansion coefficients of the SiO.sub.2 layer and semiconductor substrate.
Silicon nitride (Si.sub.3 N.sub.4) layer or multiple passivating layers of these materials are also used. These passivating layers have sufficient resistant to moisture, but in this case, these layers can not prevent the effect of polarization which is caused by the positive and negative charges in the outer shielding resin. As a result, the breakdown voltage of the PN junction is lowered, and the reliability is deteriorated by external electric fields.